Digital data transmissions over wired and wireless links sometimes may be corrupted, for instance, by noise in the link or channel, by interference from other transmissions, or by other environmental factors. Even with clear communication channels, which lend themselves to high data rates, it may not be possible to appropriately decode the data stream with the requisite error rates. In order to solve this problem, many current communication systems employ an automatic repeat request (ARQ) scheme for retransmission. In such systems an opportunity exists for requesting that data be retransmitted upon detection of an error by transmitting a negative acknowledgment (NAK) or an acknowledgment (ACK) back to the transmitter.
In more complex systems a hybrid ARQ scheme is employed. In systems employing a hybrid ARQ (HARQ) scheme, a receiver combines previously received erroneous transmissions of a packet of information with a newly received transmission in an effort to successfully ascertain the true contents of the packet. In other words, coded bits received on a first erroneous transmission are stored by the receiver and combined with the coded bits received on later transmissions thereby increasing the likelihood of a correct decoding on later transmissions. Similarly the coded bits received on the second or later transmissions are stored for combining with subsequent received bits.
Currently for HARQ schemes, when a NAK is received by the transmitter in error (misinterpretation error), the upper layer ARQ scheme is the only way to fix the error. This is because the HARQ procedure cannot detect the error since the transmitter assumes an ACK is received and starts to transmit new data, clearing the old data. There are several obvious disadvantages when performing upper layer ARQ. One disadvantage is that the upper layer ARQ incurs more delay than HARQ. Additionally, upper-layer ARQ utilizes more overhead when compared with the NAK/ACK transmission of HARQ. Finally, the upper ARQ scheme provides no combining capability between the original transmitted data and the retransmitted data. This loses the power combining gain compared with the HARQ scheme. As is evident, a need exists for a method and apparatus for performing ARQ that reduces the number of misinterpretation errors.